Recently, the market for NAND flash memories has been rapidly expanding due to increased memory capacity and reduced cost. However, NAND flash memories have the problem of increased processing cost due to the limit of miniaturization and the shrinkage of the minimum line width. As a novel nonvolatile memory for solving this problem, a resistance change memory is under development.
The resistance change memory is a nonvolatile memory reversibly switched between a high resistance state and a low resistance state by, for instance, application of voltage to a metal oxide film sandwiched between an upper electrode and a lower electrode.
In a technique for the resistance change memory, at write time for changing the resistance value from the high state to the low state, the resistance value is set to a plurality of different levels to store information having three or more values (see, e.g., JP 2007-328857(Kokai)). In another technique, during the change from one reset state (high resistance state) to two or more set states (low resistance states), the current is adjusted to control the resistance state (see, e.g., JP-A 2006-135335(Kokai)).
However, in these techniques of setting the resistance value to a plurality of levels at write time for changing the resistance value from the high state to the low state, an active element such as a transistor is required to limit the current at write time. This complicates the configuration and interferes with increasing the memory density. Furthermore, the voltage at write time typically has large variations and is difficult to control.